Multiple sclerosis (MS) is a chronic neurological disease which affects young adults at a time of maximum personal, professional and social growth (Mayo et al., 2013). The most common symptoms in MS are muscle weakness, spasticity, excessive fatigue, depression and anxiety, associated with neurodegenerative processes that can generate a vicious cycle of reduced mobility and decreased physical activity (White and Castellano, 2008). The reduction in physical activity increases the risk of secondary diseases such as obesity or cardiovascular disease (Borkoles et al., 2008). At the psychological level, symptoms reduce participation in activities of daily living and thus affect leisure and social relations (Wojcicki et al., 2014). Symptoms may appear suddenly, have a variable course and severity, and may have a devastating effect on health and quality of life over time (Latimer-Cheung et al., 2013; Mayo et al., 2013).

Technological advances to diagnose MS and the emergence of new treatments have helped to improve some forms of the disease course (Miller and Rhoades, 2012). Together with these developments, there is a clear need for strategies that allow patients to enjoy the highest possible quality of life, in accordance with their personal characteristics and with the evolution of the disease. In this regard, it has been suggested that the early initiation of an active lifestyle and exercise in patients with MS could promote neuroprotection, neuroregeneration and neuroplasticity (White and Castellano, 2008).

People with MS present impairments in functional capacity due both to the irreversible effects of the disease and to the reversible effects caused by an inactive lifestyle (Dalgas et al., 2008). However, previous studies have shown that MS patients tolerate exercise well (Padgett and Kasser, 2013); programmed physical exercise is a safe and efficient way of improving quality of life in these patients (Dalgas et al., 2008), optimizing daily functioning and enhancing their participation in different areas of daily life (Padgett and Kasser, 2013). Thus, physical exercise has been proposed as an essential component in clinical management in MS patients (Motl et al., 2011). Recently, the American College of Sports Medicine (American College of Sports Medicine, 2017) has recommended that adults with minimal disability (EDSS 0-2.5) should perform aerobic exercise 3-5 days/week, resistance exercise 2 days/week and flexibility exercise 5-7 days/week.

The aims of this study were to: 1) determine the feasibility of delivering two different structured physical exercise interventions in MS patients [(i) a combined face-to-face high-intensity interval training (HIIT) plus home exercise program and (ii) a home-based exercise program], and 2) assess the effects of these interventions on the clinical evolution, psychological wellbeing, quality of life, fatigue, cardiorespiratory fitness, strength and balance in MS patients.

The groups followed distinct schedules throughout the 40-weeks of the study. While the CG continued their usual pharmacological treatment and the same lifestyle, the CFTFG and HG continued their usual pharmacological treatment but also participated in physical exercise programs. These programs encouraged CFTFG and HG participants to include exercise in their daily lives in order to improve their physical and functional capacities. The programs also educated patients in the practice of physical exercise in accordance with their abilities and needs. In addition, the exercise programs were developed to improve the health-related physical fitness components, prioritizing endurance and strength training (Appendix 1, 2 and 3).

CFTFG: during the first 20 weeks, supervised sessions were performed twice per week and were carried out at the health centre while 4 sessions were carried out at home. The duration of the supervised session was 1.5 hours and the duration of the home session incremented from 15 min (weeks 1 to 4) to 1.5 hours (weeks 17 to 20). During the second 20-weeks period, participants exercised independently at home (Figure 2).

HG: the home-based exercise group performed 6 training sessions per week at home throughout the duration of the study (40 weeks). The duration of each session was 1.5 hours. During the first four weeks the participants attended one weekly session at the health centre where they were taught the exercises that formed the basis of the program. After these four weeks, they attended two more refresher sessions (weeks 12 and 20). From week 20 onwards they continued exercising independently at home (Figure 2).

Each participant from CFTFG and the home-based exercise group received a fit ball (O'Live Fitness Ball [R]. Aerobic & Fitness. Barcelona. Spain) and two latex exercise bands with different levels of resistance (Thera-Band [R] The hygienic Corporation. Akron. OH).

During the first 20 weeks, the aerobic training during the face-to-face sessions of the CFTFG group included HIIT on a stationary bicycle. The training load was adjusted according to the results obtained on a test carried out every four weeks, at an intensity of 17/18 on the Borg scale (Borg, 1990). Participants were able to achieve these intensities when training at home. The HIIT was complemented with aerobic sessions at an intensity of 13-15 on the Borg scale. In the HG, the intensity increased from 50% to 85% of the maximum age-predicted heart rate.

In both groups, the strength training was carried out using two latex exercise bands (red or green) (Thera-Band [R] The Hygenic Corporation. Akron. OH) and/or bodyweight resistance exercise. These exercises developed the large muscle groups of the trunk and the lower and upper limbs. The endurance and strength training was complemented with exercises for joint mobility, balance (mainly static), stretching exercises and body awareness work.

During these 40 weeks, attendance at the sessions and meetings was recorded in both groups, and the home sessions were monitored by the use of an activity band (Polar Loop. Polar Electro. Finland). Additional information was also obtained from e-mail questionnaires (Google forms. Google Inc. Mountain View. California).

Testing procedures

All participants underwent three evaluations: the first prior to start the intervention (E1), the second after 20 weeks (E2) and the third after 40 weeks (E3). These evaluations comprised clinical and neurological assessments, quality of life and fatigue scales [the Modified Fatigue Impact Scale (MFIS)], Hospital Anxiety and Depression scale (HAD) and Functional Assessment of Multiple Sclerosis (FAMS), and a maximal cardiorespiratory fitness test. Lower limb strength and balance test were assessed prior to the intervention and after 20-weeks.

Anthropometric measurements

Height was measured to the nearest 0.1 cm by using a stadiometer (Seca 225, Seca, Hamburg, Germany).Weight was measured to the nearest 0.1 kg on a digital scale (Tanita MC-780U, Arligton Heights, IL, USA) with the participants wearing light weight clothing and no shoes. Body mass index (BMI) was calculated as weight in kilograms divided by height in meters squared (kg/[m.sup.2]).

Clinical and neurological assessments

The participants' neurological impairment and degree of disability were assessed with the EDSS and the number of acute exacerbations of MS symptoms.

Feasibility evaluation criteria

Feasibility was measured as the adherence to the exercise program, and completion rates to the program. Adherence represented the percentage of participants who performed the programmed sessions. Completion rate represents the percentage of participants out of the total participants that completed the study.

Questionnaires

Psychological wellbeing: The 14-item HAD questionnaire measures the degree of anxiety and depression. HAD has often been used in patients with chronic fatigue syndrome (McCue et al., 2006).

Fatigue: The 21-item MFIS (Fisk et al., 1994) questionnaire is based on interviews with MS patients concerning the impact of fatigue on their lives.

Quality of life: The FAMS is a multidimensional self-report scale designed specifically to measure the quality of life of people with MS. Each participant was assessed by means of the Spanish version of the FAMS scale (Chang et al., 2002).

Cardiorespiratory fitness test

All tests were conducted in the morning at a room temperature of 22 to 24[degrees]C and a relative physical humidity of 55 to 65%. The participants were tested on a precalibrated cycle ergometer (Excalibur, Lode, Groningen, the Netherlands), cycling at 50 rpm. After a 4-min period cycling at 0 W, participants followed a 20 W/min ramp protocol up to exhaustion. V[O.sub.2]peak (L/min), relative V[O.sub.2]peak (ml/kg/min) and respiratory exchange ratio (RER) were measured through breath-by-breath with an automatic gas analysis system (Metasys TR-plus, Brainware SA, La Valette, France) equipped with a pneumotachometer and using a two-way mask (Hans Rudolph, Kansas, USA). Gas and volume calibrations were performed before each test, according to the manufacturer's guidelines.

The participants were asked to sit down and stand upright as often as possible for 30 s without using their hands. The instructors did not record the result if participants could not stand up from a chair without supporting themselves with their arms on arm rests, knees...